Field of the Disclosure
The present disclosure relates to a display device, and more particularly, to an array substrate and a display panel having the same. Although the present disclosure is suitable for a wide scope of applications, it is particularly suitable for suppressing defects resulted from light leakage, insufficient liquid crystal, impact, etc., in the array substrate of the display panel.
Description of the Background
A display device essentially comprises a display panel, which includes an array substrate, a color filter substrate, and a liquid-crystal layer interposed between the array substrate and the color filter substrate. When electric field is applied across the display panel, the orientation of the liquid-crystal molecules in the liquid-crystal layer is changed, such that difference in transmittance is implemented.
Along with such difference in transmittance, combinations of color are reflected on light produced from a backlight disposed at the rear side of the display panel as the light passes through color filters, thereby representing color images.
Processes of fabricating such a display device include a substrate-fabricating process of fabricating an array substrate and a color filter substrate, a cell process of completing a display panel, and a module process of assembling the display panel and a backlight.
During the substrate-fabricating process, a series of process steps such as thin-film deposition, photolithography, and etching are repeated, so that an array layer and a color filter layer are implemented on the substrates. Subsequently, during the cell process, a seal pattern is formed on the array substrate or the color filter substrate for attaching the substrates to each other, and then the array substrate and the color filter substrate are attached together with a liquid-crystal layer filled therein, thereby completing a display panel. Thereafter, a polarizer plate, a driving circuit, etc., are attached to the display panel during the module process and then the display panel is assembled with a backlight, thereby implementing a display device.
In addition, spacers are inserted between the array substrate and the color filter substrate so as to maintain a gap therebetween.
The spacers may include ball spaces and column spacers, depending on the shape and processes of forming them. The ball spacers are formed by being sprayed on the array substrate or the color filter substrate. The column spacers are formed by being patterned on the array substrate or the color filter substrate. Since the column spacers can be formed at desired positions in a desired shape, it has been more preferred. The column spacers are typically formed on the color filter substrate, which undergoes the lesser number of processes than the array substrate.
Hereinafter, an in-plane switching mode display panel will be described in detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view of an in-plane switching mode display panel. FIG. 2 is a plan view of a color filter substrate shown in FIG. 1.
Referring to FIGS. 1 and 2, an in-plane switching mode display panel 1 includes an array substrate 10, a color filter substrate 50 facing the array substrate 10 and attached to each other, and a liquid-crystal layer LC disposed between the array substrate 10 and the color filter substrate 50 to fill the space therebetween. A plurality of pixel areas P is defined on each of the array substrate 10 and the color filter substrate 50.
The array substrate 10 includes a plurality of gate lines (not shown) extended in a first direction of a lower substrate 11, a plurality of common lines (not shown) extended in parallel with and spaced apart from the plurality of gate lines, a plurality of data lines (not shown) extended in a second direction intersecting the first direction, and a plurality of thin-film transistors T each disposed at the respective intersections between the gate lines and the data lines.
The thin-film transistor T includes a gate electrode 20, a gate insulation film 25 covering the gate electrode 20, a semiconductor layer 22 disposed on the gate insulation film 25 and overlapping the gate electrode 20, and a source electrode 24 and a drain electrode 26 disposed on the semiconductor layer 22 and spaced apart from each other. A contact hole 37 is formed via which a portion of the drain electrode 26 is exposed. A pixel electrode 40 is connected to the drain electrode 26 via the contact hole 37.
In addition, the array substrate 10 includes a protective layer 35 covering the plurality of data lines, the source electrode 24 and the drain electrode 26, and a lower alignment film 15 covering the pixel electrodes 40 and the common electrodes 45. The pixel electrode 40 and the common electrode 45 are formed of a transparent material so as to increase an aperture ratio.
The color filter substrate 50 includes: an upper substrate 51; a black matrix 60 corresponding to the plurality of gate lines, the plurality of common electrode, the plurality of data lines and the plurality of thin-film transistors T; red, green and blue color filters 70a, 70b and 70c sequentially disposed in the plurality of pixel areas on the upper substrate 51 and the black matrix 60, respectively; and an upper alignment film 65 covering the red, green and blue color filters 70a, 70b and 70c. 
Although not shown in the drawings, the color filter substrate 50 further include an overcoat layer disposed between the red, green and blue color filters 70a, 70b and 70c and the upper alignment film 65.
The liquid-crystal layer LC is operated by the electric field horizontally applied though the pixel electrodes 40 and the common electrodes 45.
As described above, the liquid-crystal layer LC is disposed between the array substrate 10 and the color filter substrate 50 to fill the space therebetween. A column spacer 80 is formed between the array substrate 10 and the color filter substrate 50 to maintain a cell gap therebetween.
The column spacer 80 is formed by being patterned on the substrate 10 or the color filter substrate 50, frequently on the color filter substrate 50 which undergoes the lesser number of processes. The column spacer 80 is typically disposed where it overlaps the black matrix 60, more specifically, the thin-film transistor T.
When external force is applied to the in-plane switching mode display panel 1, the array substrate 10 or the color filter substrate 50 can be moved horizontally. As a result, the column spacer 80 is also moved to the left or the right side with respect to the thin-film transistor T.
When this happens, the surface of the lower alignment film 15 near the column spacer 80 can be damaged as the column spacer 80 is moved, and accordingly light leakage (i.e., red eye defect) can occur in the in-plane switching mode display panel 1.
That is, if the column spacer 80 is moved to the pixel area P by external force such that a scratch is formed on the surface of the lower alignment film 15 covering the protective layer 35 of the array substrate 10, the portion of the lower alignment film 15 near the column spacer 80 loses alignment property. Accordingly, the polarization properties of the liquid crystals located at the portion of the alignment film become different from the normal portions, thereby resulting in a red eye defect.
To increase the transmittance of the display panel 1, there is ongoing effort to gradually reduce the line width of the column spacer 80 and the line width of the black matrix 60. However, when the line width of the black matrix 60 is reduced, there is a problem in that a failure rate is increased due to the movement of the column spacer 80.
In addition, the contact hole 37 formed in the array substrate 10 can contribute to a defect during the process of forming the lower alignment film 15. The lower alignment film 15 is applied on the surface of the array substrate 10 by transferring a polyimide resin with a mask.
However, the contact hole 37 is a recessed portion of the array substrate 10, and if the contact hole 37 is not completely filled with the transferred polyimide solution, the thickness of the portion of the alignment film 15 near the contact hole 37 can be insufficient.
In addition, the contact hole 37 can be the main cause of the defect during the process of filling the space between the color filter substrate 50 and the array substrate 10 with liquid crystals.
The space between the color filter substrate 50 and the array substrate 10 can be filled with liquid crystals. The amount of the liquid crystals has to be appropriate. If the amount is insufficient, light leakage occurs. If the amount is excessive, yellow mura occurs. The volume between the color filter substrate 50 and the array substrate 10 is calculated theoretically, and the liquid crystals are applied by the amount corresponding to a certain percentage of the theoretically-calculated volume.
However, the shape of the contact hole 37 may vary depending on the thermal process for curing the protective layer 35. If the shape of the contact hole 37 changes, the cell gap is changed, resulting in a substantial change in the volume of the space filled with liquid crystals. As a result, the amount of the liquid crystals becomes problematic, contributing to defect on the display panel.
In view of the above, aspects of the present disclosure provide a structure that can suppress defects resulted from the contact hole and the column spacer in a display panel.